Plunger assembly for hydraulic cylinder

ABSTRACT

A hydraulic cylinder includes piston and plunger assemblies fitted together with a retention ring. This design allows finish-machined pistons to be assembled without welding of semi-finished machine components.

FIELD OF THE INVENTION

[0001] This invention relates to the field of hydraulic cylinders and, in particular, to piston and plunger assemblies in hydraulic cylinders.

BACKGROUND OF THE INVENTION

[0002] Hydraulic cylinders are well known in the art. Conventional hydraulic cylinders include an outer cylinder capped at both ends. A piston is movably disposed in the cylinder. A hollow piston rod, or a plunger tube, in also movably disposed within the cylinder. As hydraulic pressure builds, the piston is moved, which in turn moves the plunger tube.

[0003] The connection between the piston and the plunger tube can be made in a variety of ways known in the art. Welding is the most common connection means in telescopic hydraulic cylinders. The working efficiency of welding is low and it is difficult to remove spatter resulting from welding. Residual spatter may give rise to serious defects in the operation of the hydraulic cylinder. U.S. Pat. No. 5,960,696, issued to Niwa et al., addresses this concern, disclosing a device that includes a pipe in a spigot portion of the piston. The pipe is press fit into the interior of the spigot portion rather than welded. The press-fit pipe is included in the spigot portion to allow oil to flow through the pipe into a reservoir from an oil passage in the piston. It is intended to dispense with the pipe welding work and prevent contamination that results from welding. However, the patent does not address the connection between the piston and the plunger tube.

[0004] The normal process for plunger assemblies is to weld semi-finished machined components and follow up with a finish operation. This process is not only inefficient because of the welding, but also extra time is required by the finish operation. The problem is magnified in multi-stage telescopic cylinders. Ideally, an assembly process would allow for finish-machined parts to be assembled without separate assembly (welding) and finishing steps.

[0005] Therefore, what is needed is a hydraulic cylinder assembly that does not utilize welding in the assembly process. An improved connection between the piston and the plunger tube is also required. A process for assembling hydraulic cylinders that reduces time and cost is also needed.

SUMMARY OF THE INVENTION

[0006] The present invention is a hydraulic cylinder with a close fitted piston over a plunger tube. The close fitting replaces any welding needed to connect the piston and the plunger tube. A retention ring is used in conjunction with the close fitting to retain the piston.

[0007] Each cylinder can include several plunger tube assemblies of varying diameters and lengths to make up a complete hydraulic cylinder. A piston is pre-machined to size, to match the corresponding plunger, and locked into position about the plunger. A spring tension split ring is incorporated to retain the piston. This retaining ring also helps carry the load placed on the piston. The plunger tube is provided with an oil hole to allow oil to pass from plunger to plunger for normal cylinder operation.

[0008] Therefore, it is an aspect of this invention to provide a hydraulic cylinder that does not use welds to attach the piston to the plunger tube.

[0009] It is another aspect of the invention to provide an improved connection between a piston and a plunger tube.

[0010] It is yet another aspect of the invention to utilize a close fit with a retaining ring between the piston and the plunger tube.

[0011] It is a further aspect of the invention to provide an assembly for a hydraulic cylinder with a substantially reduced process time.

[0012] It is a further aspect of the invention to allow machine finished pistons to be assembled and substantially eliminate the need for a follow up machine finish operation.

[0013] These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the appended claims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a cross sectional view of a plunger tube assembly used in the present invention.

[0015]FIG. 2 is an isometric view of the plunger tube assembly shown in FIG. 1 detailing the insertion slot in use with the present invention.

[0016]FIG. 3 is an isometric view of a telescopic hydraulic cylinder, a preferred embodiment of the present invention.

[0017]FIG. 4 is a side view of a telescopic hydraulic cylinder in use with a dump body.

DETAILED DESCRIPTION OF THE INVENTION

[0018]FIG. 1 shows plunger tube assembly 10. Plunger tube assembly 10 is selected from a variety of diameters and lengths to be movably inserted into the telescopic hydraulic cylinder shown in FIG. 3. A telescoping hydraulic cylinder will use several plunger tube assemblies 10, each of differing diameter, in normal operation. The different diameters allow the telescoping cylinder to collapse upon itself when not in use.

[0019] Piston 14 is pre-machined to size, specifically dimensioned to slide over plunger tube 12. Piston 14 is close fitted over plunger tube 12. In this manner, plunger tube 12 and piston 14 fit together to form plunger assembly 10. Piston 14 includes piston locating surface 15, which is a close sliding fit incorporated to align piston 14 on plunger tube 12. Because of the close fitted piston, retained by retention ring 16, no welds are required in the assembly process.

[0020] After piston 14 is slid into position, retention ring 16 is inserted between piston 14 and plunger tube 12 through slotted opening 18 in piston 14. Retention ring 16 maintains the position of piston 14 about plunger tube 12. Retention ring 16 carries loads placed on piston 14 at piston centering surface 20. Loads at piston locating surface 22 are carried by the end of plunger tube 12. Piston surface 38 carries the thrust of plunger assembly 10 during extension. As each plunger is fully extended the load shifts to piston centering surface 20. This surface locates plunger assembly 10 in a center position when fully extended from one plunger to another. The load on this surface is carried by retention ring 16.

[0021] In the preferred embodiment, piston 14 includes slotted opening 18, as seen in FIG. 2. Slotted opening 18 is located directly over retention ring 16. When installing piston 14 over plunger tube 12, slotted opening 18 is used to insert retention ring 16 in its correct location.

[0022] To assist in the installation of piston 14, piston chamfer 26 is included. Piston chamfer 26 is an angular chamfer located near piston centering surface 20. The angular chamfer is incorporated to assist in installing piston 14 about plunger tube 12.

[0023] Multiple plunger assemblies 10 with plunger tubes 12 of varying diameters can be incorporated into a telescopic hydraulic cylinder 30, as shown in FIG. 3. FIG. 3 demonstrates the exterior of telescopic hydraulic cylinder 30 when extended. Plunger assembly 10 is located in cylinder 32. Plunger assemblies of smaller diameters (not shown) are located in cylinders 34. FIG. 4 demonstrates extended telescopic hydraulic cylinder 30 in use with dump body 36.

[0024] To extend telescopic hydraulic cylinder 30, oil is introduced in to cylinder 32. Hydraulic pressure is built up and pushes against piston end 38, shown in FIG. 1. The hydraulic pressure pushes against this surface when extending each plunger. When closed, each plunger assembly 10 rests on piston end 38. Piston stop 40 receives piston end 38 of the succeeding plunger. When closed, each succeeding plunger assembly 10 will rest against piston stop 40.

[0025] In a telescopic hydraulic cylinder with multiple plunger assemblies, plunger tube 12 includes plunger oil hole 42. Plunger oil hole 42 allows oil to pass from plunger to plunger for normal cylinder operation. Once plunger tube assembly 10 is fully extended, oil (not shown) passes through plunger oil hole 42 to reach the next plunger assembly (not shown). Hydraulic pressure then pushes on the piston end (not shown) of the succeeding plunger, extending the succeeding plunger.

[0026] Wear guide groove 44 is also included in the preferred embodiment. A non-metallic wear ring (not shown) is installed in wear guide groove 44. The wear ring prevents metal-to-metal scoring between plunger tube assemblies as hydraulic pressure extends each plunger tube assembly 10.

[0027] Because of the close fit of piston 14 and retention ring 16 about plunger tube 12, no welding steps are needed to assemble plunger assembly 10. In the preferred embodiment, machine finished pistons are used for piston 14 so that no additional finishing step is required. The process time for a typical 6″ three stage cylinder using the present invention is reduced by approximately 30% over traditional methods of welding and including an additional finishing step.

[0028] Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein. 

What is claimed is:
 1. A plunger assembly for a hydraulic cylinder, said plunger assembly comprising: a plunger tube; a piston dimensioned to slide fit over said plunger tube; and an inserted retention ring disposed about said plunger tube between said piston and said plunger tube; wherein said piston is slid in position over said plunger tube, and wherein said inserted retention ring retains said piston and carries loads placed on said piston.
 2. The plunger assembly as claimed in claim 1, wherein said piston further comprises an end having a chamfer, and wherein said chamfer assists said piston to slide over said plunger tube.
 3. The plunger assembly as claimed in claim 1, wherein said piston further comprises an insertion slot disposed over said inserted retention ring, and wherein said inserted retention ring is disposed about said plunger tube by inserting said inserted retention ring into said insertion slot.
 4. The plunger assembly as claimed in claim 1, wherein said plunger tube further comprises an oil hole and an interior and exterior, and wherein said oil hole allows oil to pass from said exterior to said interior of said plunger tube.
 5. The plunger assembly as claimed in claim 1, wherein said piston comprises a machine finished piston.
 6. A plunger assembly for a hydraulic cylinder, said plunger assembly comprising: a plunger tube; a piston dimensioned to slide onto said plunger tube, said piston having an end with a chamfer, and a close fit about said plunger tube; a retention ring disposed about said plunger tube between said piston and said plunger tube; and an insertion slot in said piston disposed over said retention ring; wherein said retention ring is disposed about said plunger tube by inserting said retention ring into said insertion slot, and wherein said chamfer assists said piston to slide over said plunger tube, and wherein said retention ring retains said piston about said plunger tube.
 7. The plunger assembly as claimed in claim 6, wherein said plunger tube further comprises an oil hole and an interior and exterior, and wherein said oil hole allows oil to pass from said exterior to said interior of said plunger tube.
 8. A telescoping hydraulic cylinder apparatus comprising: a plurality of cylinders; and a plunger assembly disposed inside each of said plurality of cylinders, said plunger assembly comprising: a plunger tube; a piston dimensioned to slide fit over said plunger tube; a piston stop at an disposed at an end of said piston; and an inserted retention ring disposed about said plunger tube between said piston and said plunger tube; wherein said piston is slid into position over said plunger tube, and wherein said inserted retention ring retains said piston and carries loads placed on said piston, and wherein said piston stop receives said plunger assemblies from said plurality of cylinders when said telescoping hydraulic cylinder is closed.
 9. The telescoping hydraulic cylinder apparatus as claimed in claim 8, wherein said plunger assembly further comprises an insertion slot in said piston disposed over said inserted retention ring, and wherein said inserted retention ring is disposed about said plunger tube by inserting said inserted retention ring into said insertion slot.
 10. The telescoping hydraulic cylinder as claimed in claim 9, wherein said piston further comprises a wear guide groove, and wherein said wear guide groove accepts a wear ring to prevent scoring between each said plunger tube assembly. 